202 F. A. Genth — Contributions to Mineralogy. 



calcite was deposited upon the same, because, when broken off 

 from the cacoclasite, it shows the reverse of the grooves and 

 corrugations of the latter. 



For investigation two crystals were used, the best one of 

 Professor Hoffmann's (I) about 12 mm in size, was almost white, 

 but had a little pyrite in the center, that from Dr. Foote, (II) 

 about 18 mm long had a slightly brownish white color, but the 

 interior was of a uniform grayish white color. Finely granu- 

 lar, like sugary quartz and of the same luster, crystal I was 

 slightly coarser than II. Spec. grav. of crystal 1=3*337, of 

 crystal II =3-222. 



They were broken into small fragments from 2 to 3 mm in 

 diameter and carefully examined for their purity, but none 

 showed any admixture of blue calcite or other minerals. 



By qualitative analysis it was found that although no calcite 

 could be found by a strong lens, both crystals contained a car- 

 bonate, probably that of calcium, a phosphate, probably apatite, 

 and a considerable quantity of free quartz. In the quantita- 

 tive analysis the latter was determined by fusing the finely 

 powdered mineral with microcosmic salt, dissolving in hydro- 

 chloric acid and boiling the remaining silica with dilute sodium 

 hydrate, as long as it extracted soluble silica. 



In crystal I the remaining Si0 2 was 23-44 per cent ; this on 

 being fused with sodium carbonate etc., etc., gave pure Si0 2 = 

 23 "04 per cent present as quartz, with little alumina and 

 calcium oxide. Crystal II treated in the same manner gave 

 11*84 per cent of silica which contained 11*63 per cent of 

 pure Si0 2 present as quarts. The analyses gave the following 

 results : 



I. II. 



H 2 = 1*04 2*28 



C0 2 6*73 4*25 



SiO„ 31*52 32*67 



P 2 5 2*19 3*36 



A1 2 3 17*34 1 9*63 



Fe 2 3 0*51 0-39 



MgO trace. 0*49 



CaO 40*95 36*38 



Na 2 trace. 0*31 



K.O. trace. 0*20 



100*28 99.96 



Deducting the C0 2 as calcium carbonate, the P 2 5 as apatite 

 and the free quartz, we get : 



CaC0 2 = 15*20 9*66 



Ca 5 F[POJ 3 5*05 7*74 



SiO„- -.. 23*04 11*63 



Apparent admixtures 43*29 29*03 



